An embodiment is for determining a region of interest to be rendered in an ultrasound volume data set of an interior of an object under examination. In an embodiment, the method includes: determining a projection position in a two dimensional X-ray projection image of the object under examination, wherein a projection ray correlated to the projection position passes through the region of interest; and extracting a partial data set encompassed by the ultrasound volume data set using the projection position determined and based upon geometrical information relating to the X-ray 3D ultrasound unit.